This invention relates to a semiconductor device and a process of manufacturing the same. Particularly, the invention concerns a high frequency high output bipolar transistor and a process of manufacturing such a transistor.
In order to increase the power gain of high frequency high output bipolar transistors at high frequencies, there have been previously proposed various means designed to decrease the base resistance thereof. For example, there have been already known a graft base structure including an active and an inactive base region, a structure including a emitter region encircled by a base region, a multi-emitter structure (which is also called a teeth of comb structure) having emitter stripes which are very narrow in width and others. Also, in order to decrease the capacitance of the base-to-collector junction, there has been previously proposed a measure of decreasing an impurity concentration of the particular semiconductor region toward which a depletion layer from the base-to-collector junction spreads.
In conventional bipolar transistors, as described above, the base-to-collector junction has extended substantially over the entire area of a semiconductor wafer involved, resulting in the disadvantage that the capacitance of the external base-to-collector junction is particularly large. Isoplanar silicon bipolar transistors, which are commercially available, have been improved with respect to this disadvantage by effecting the insulator width isolation of the inactive base region continuous to the base-to-collector junction through the utilization of the selective oxidization. However, the manufacturing of such transistors has included manufacturing steps which are complicated. Also, in their manufacturing, an erosion effect called "bird beak" might partly occur in the silicon of the transistors. This bird beak is apt to permit either end of the emitter region to extend over the mating base region to be connected to the collector region. Even though the emitter region would not be connected to the collector region, it has been difficult to control the base width.
Accordingly, it is the principal object of the present invention to eliminate the disadvantages of the prior art practice as described above by the provision of a semiconductor device capable of decreasing sharply the capacitance of a base-to-collector junction involved in a relatively easy manner and also of a process of manufacturing such a semiconductor device.
It is an object of the present invention to provide a semiconductor device designed and constructed so as to decrease sharply its base resistance and a process of manufacturing such a semiconductor device.
It is another object of the present invention to provide a process of manufacturing semiconductor devices which are consistently uniform with a good reproducibility.